1. Field
The present disclosure relates to the movement of irrigation systems and more particularly pertains to a new system and method for moving spans of an irrigation system for providing the benefits of variable rate irrigation according to a prescription while providing more familiar local control to the operator in the field.
2. Description of the Prior Art
In a conventional mechanized irrigation system, a fluid application rate may be selected at which the fluid (typically water) applied to the field is controlled as a percentage of a maximum base movement rate. (The fluid application rate is sometimes expressed in terms of a fluid application depth, which is a measurement of the vertical depth of the fluid, applied by a single rotation of the irrigation system, that would cover the irrigated area of land if there was no drainage or ground absorption to dissipate the fluid.) The water flows through the irrigation system at essentially a constant and uniform rate, and the fluid application rate is thus controlled by controlling the rate of movement of the irrigation system in the field, such as by the rate of rotation of a center pivot irrigation system. However, the rate of movement of the irrigation system is typically not a uniform speed of constant movement that is maintained as the irrigation system moves over the field, but rather a cycle of alternating periods of moving the irrigation system and stopping the movement of the irrigation system as the irrigation system operates (and the water flows). The relationship between the time period of movement and time period of stopping controls the overall rate of movement or speed of the irrigation system, and thus the overall water application rate (or depth).
The rate at which the water is applied to the field is commonly referred to as a percentage of the maximum rate at which the irrigation system moves over the field. The percentage, percent rate or speed also is an indication of the percentage of time that the center pivot span is moving or rotating, with the balance being time that the irrigation system is stopped. For example, the percentage, percent rate or speed indicates the percentage of a particular time frame that the span of the irrigation system is moving and rotating about the center. For example, a 75 percent rate indicates that 75 percent of one minute (e.g., 45 seconds), the span is moving, and the remainder of the time (e.g., 15 seconds) the span is stationary. The more time that the irrigation system is moving, the “faster” the center pivot span rotates about the field (speed), and the less water that is applied to a particular location in the field and, therefore, the lower the water application rate Conversely, the less time that the irrigation system is moving (and is stopped), the “slower” the center pivot span rotates about the field (speed), and the more water is applied to a particular location in the field, thus increasing the water application depth. In other words, the more time that the irrigation system spends rotating, the more ground that the span covers in a given time period having dispensed the same amount of water. The water application rate control may allow the user to select a setting that directly correlates to a percent rate and the control may be calibrated in terms of the water application depth and is often expressed in inches, centimeters or millimeters. The rate control may include a device located at the control panel or a secondary remote control device of the irrigation system. The rate setting selected by the user then typically moves the irrigation system at the same rate for an entire revolution of the span.
The conventional irrigation system control set forth above is typically set with a single value to control the base movement rate, or the uniform water application rate or depth, for the entire field, and not for the immediate area under the span. Thus, there is no variation in the rate of movement or speed as the span rotates over field locations where the soil texture, i.e., water holding capacity, or the topography of the field vary, and therefore the water application depth requirements vary.
Systems have been devised for varying the local movement rates at which the water is applied to the field at various angular positions or degrees of the spans of the irrigation system from the center point. These systems typically employ the use of a local movement rate prescription or table of values that is uploaded to the irrigation system, and the values set the local movement rates or speeds at the various (angular) locations in the field. The values in the table, however, only reflect a single base movement rate which has been adjusted for the local water application rates or depths applicable to that field. In other words, while the local movement rate about the field will vary according to the values in the table, the values in the table typically reflect a percentage adjustment of one particular base movement rate (such as 50 percent).
Therefore, in such systems, in order for the operator/farmer to change the base movement rate at which water is generally applied to the field, such as based upon general moisture conditions (e.g., whether it has rained recently or the weather has recently been particularly warm or forecasted to be warm, or whether the average soil moisture content is high or low), a different table of values must be uploaded that is based upon both the local movement rate adjustment and the (new) base movement rate selected by the operator/farmer.